The combustion of sulfur-containing fuels generates significant amounts of sulfur dioxide (SO.sub.2). Oxides of nitrogen (NO.sub.x) are also often generated in the course of the combustion of various fuels. Without appropriate treatment of the exhaust gases of combustion, large amounts of sulfur and nitrogen oxides would be injected into the atmosphere, causing a variety of ecological problems.
Various processes have been developed to remove SO.sub.2 and NO.sub.x from exhaust gases. Ozone has been used to oxidize nitrogen oxides in waste gas streams, e.g., in the process of U.S. Pat. No. 4,035,470. Olefins have been used in a gas phase process for removing sulfur dioxide from gases, e.g., in the process of U.S. Pat. No. 4,191,732. Electron beam irradiation has been used to activate nitrogen and sulfur oxides, followed by reaction with ammonia, e.g., in the process disclosed by Kawamura et al., Environ. Sci. Tech., 14, 288 (1980).
Studies of the oxidation of sulfur dioxide in the atmosphere have been reported by Cox et al., J. Chem. Soc. Faraday Trans., 168, 1735 (1972), and by Calvert et al., Atmos. Environ., 12, 197 (1978). Both articles based their analyses on the assumption that the oxidation of sulfur dioxide proceeds through the formation of sulfur trioxide, which is then hydrated to form sulfuric acid, although Cox et al. recognized the difficulty with this assumption. Neither Cox et al., nor Calvert et al. were able to satisfactorily explain apparently inconsistent observations in the ozone-alkene-SO.sub.2 system. Accordingly, predictions based on either of their analyses would not permit control of this reaction, and in particular, would not lead to the combination of steps necessary to effect the present process. Neither Cox et al. nor Calvert et al. envisioned a process for removing SO.sub.2 from a gas stream such as an exhaust gas or flue gas stream.
A need therefore continues to exist for a simple, homogeneous gas-phase process capable of removing SO.sub.2 from a variety of gas streams including, but not limited to, exhaust gases from combustion processes.